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// Copyright 2009 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
package dns
import (
"bufio"
"net"
"os"
"strconv"
"strings"
)
// Wraps the contents of the /etc/resolv.conf.
type ClientConfig struct {
Servers []string // servers to use
Search []string // suffixes to append to local name
Port string // what port to use
Ndots int // number of dots in name to trigger absolute lookup
Timeout int // seconds before giving up on packet
Attempts int // lost packets before giving up on server
}
// ClientConfigFromFile parses a resolv.conf(5) like file and returns
// a *ClientConfig.
func ClientConfigFromFile(conf string) (*ClientConfig, error) {
file, err := os.Open(conf)
defer file.Close()
if err != nil {
return nil, err
}
c := new(ClientConfig)
b := bufio.NewReader(file)
c.Servers = make([]string, 3)[0:0] // small, but the standard limit
c.Search = make([]string, 0)
c.Port = "53"
c.Ndots = 1
c.Timeout = 5
c.Attempts = 2
for line, ok := b.ReadString('\n'); ok == nil; line, ok = b.ReadString('\n') {
f := strings.Fields(line)
if len(f) < 1 {
continue
}
switch f[0] {
case "nameserver": // add one name server
a := c.Servers
n := len(a)
if len(f) > 1 && n < cap(a) {
// One more check: make sure server name is
// just an IP address. Otherwise we need DNS
// to look it up.
name := f[1]
switch len(net.ParseIP(name)) {
case 16:
name = "[" + name + "]"
fallthrough
case 4:
a = a[0 : n+1]
a[n] = name
c.Servers = a
}
}
case "domain": // set search path to just this domain
if len(f) > 1 {
c.Search = make([]string, 1)
c.Search[0] = f[1]
} else {
c.Search = make([]string, 0)
}
case "search": // set search path to given servers
c.Search = make([]string, len(f)-1)
for i := 0; i < len(c.Search); i++ {
c.Search[i] = f[i+1]
}
case "options": // magic options
for i := 1; i < len(f); i++ {
s := f[i]
switch {
case len(s) >= 6 && s[:6] == "ndots:":
n, _ := strconv.Atoi(s[6:])
if n < 1 {
n = 1
}
c.Ndots = n
case len(s) >= 8 && s[:8] == "timeout:":
n, _ := strconv.Atoi(s[8:])
if n < 1 {
n = 1
}
c.Timeout = n
case len(s) >= 8 && s[:9] == "attempts:":
n, _ := strconv.Atoi(s[9:])
if n < 1 {
n = 1
}
c.Attempts = n
case s == "rotate":
/* not imp */
}
}
}
}
return c, nil
}
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